[5] He joined the side for the 2014–15 season, but did not link up with the squad until after Auckland had finished in the 2014 ITM Cup.
Auckland were knocked out in the semi-finals of the competition on 18 October, and McCartney made his debut for Connacht on 21 November, coming on as a replacement against Zebre in the 2014–15 Pro12.
[8] Having celebrated his 50th Connacht appearance with a Man of the Match performance and two tries against Benetton Treviso in the Guinness PRO12, McCartney secured his place at Sportsground with a 3-year extension until at least the summer of 2020.
He went on to play in his final year for Connacht in the 2019/20 season which was unexpectedly cut short due to the COVID-19 pandemic.
He played his last game for Connacht starting against Toulouse in Heineken Champions Cup at The Sportsground on 11 Jan 2020.